The present invention related to ball-like structures and contacting materials for wastewater-treatment composed of the ball-like structures, and more in particular, it relates to ball-like structures formed from bundled, crimped fibers rounded around a roughly central portion thereof as a core. The ball-like structures according to the present invention can be used suitably, for example, as contacting materials for water-treatment, materials for fish culture and filtering materials.
Ball-like structures formed from bundled, crimped fibers rounded around a roughly central portion thereof as a core are known. For instance, Japanese Utility Model Publication No. 35278/1989 proposes contacting materials for wastewater-treatment, in which crimped fine fiber yarns are bundled and bound for gathering up at a roughly central portion into a bundle which is then rounded into a spherical shape and the bound portion is embedded to the inside of the bundle.
Further, Japanese Patent Application Laid-Open (KOKAI) No. 202837/1992 proposes a method of producing ball-like structures, which comprises binding a bundle composed of a plurality of crimped fibers aligned with each substantially constant interval successively, then cutting the bundle at an intermediate portion between the resultant adjacent bound portions, and further, applying a heat-treatment to the thus obtained fiber bundles in the form of short tufts.
The ball-like structures have a large specific surface area, since the constituent fibers are entangled in a three dimensional manner to each other into a spherical shape. Such ball-like structures have an advantageous effect of providing favorable settling of microorganisms, deposition of sludges to the ball-like structures and enhancing the growth of the microorganisms, when the ball-like structures are applied to a cleaning-treatment of wastewater due to self-cleaning effect of the microorganisms as described in Japanese Utility Model Publication No. 35278/1989.
However, in a case of the ball-like structures as described in Japanese Utility Model Publication No. 35278/1989, the core at the central portion (bound portion) has a bound structure using synthetic fiber yarns, rigid plastic bands or fine metal wires, so that the synthetic fibrous yarns or rigid plastic bands incapable of providing a firmly bound structure have a drawback that fibers constituting the ball-like structures are liable to slip off through the bound portion.
The foregoing drawback causes clogging in a water-treatment bath in a case of using the ball-like structures as the contacting materials for water-treatment. Also in a case of using the ball-like structures, for example, as materials for fish culture and filtration, it also causes clogging in relevant facilities. Then, in a case of using the ball-like structures as the contacting materials for water-treatment, the slipping-off of the fibers is remarkable, particularly, upon backwashing in which the ball-like structures collide violently against each other.
On the other hand, in a case of a firm bound structure using fine wires of metal such as aluminum, although slipping-off of fibers through the bound portion can be improved, it causes an additional problem in view of waste disposal in that the fine metal wires are left after burning-treatment of the spent ball-like structures. Further, in a backwashing operation for the contacting materials used for water-treatment, an aqueous alkali or acid solution is sometimes used for improving the detergent effect. In this case, the binding member made of fine wires of metal such as aluminum can not be used because of poor chemical resistance. Moreover, in the ball-like structures using the fine metal wire as the binding member, since the diameter of the metal ring constituting the bound portion (diameter of the bound fibers) is constant, it inevitably has a drawback that the bound portion is loosened as detachment of the fibers from the bound portion occurs and the fibers slip off one by one to disintegrate the ball-like structures.
Also, the Japanese Patent Laid-Open Publication No. 202837/1992 discloses an example of ball-like structures of a bound structure using aluminum wires, but there is no detailed description for the ball-like structures having the molten-fused structure as a bound structure.
In view of the foregoing situations, as a result of earnest present inventors' studies, it has been found that ball-like structures, wherein the bundled, crimped fibers are melted and fused about at a central portion, and which satisfy the following stipulations, can be free from yarn slipping-off or yarn disconnection and can be served for practical use.
(a) A density of the molten-fused structure is not less than 75% based on a density of the crimped fibers constituting the ball-like structures. PA1 (b) A length of the molten-fused structure is 5 to 50% based on a diameter of the ball-like structures. PA1 (c) A withdrawing strength of the crimped fiber strand connected to the molten-fused structure is not less than 50% based on a linear strength of the crimped fiber strand itself used for the ball-like structures. PA1 (a) a ratio of the specific gravity of the molten-fused fibers forming the ball structures divided by the specific gravity of the material that forms the fibers, expressed as a percentage, is at least 75%, PA1 (b) a length of the molten-fused structure is 5 to 50% based on a diameter of the ball-like structures, and PA1 (c) a withdrawing strength of a crimped fiber strand connected with the molten-fused structure is not less than 50% based on a linear strength of the crimped fiber strand itself used for the ball-like structures.
The present invention has been accomplished based on the above-mentioned finding.